New Timer Unit

Added a timer unit to the IOP16. The timer unit allows a time value to be written to the Timer and the timer can be polled from the IOP16 to determine when the time has elapsed.

The timer unit can count in uSecs (0-255), mSecs (0-255) or Seconds (0-255). Writing the appropriate time value to the timer unit starts the timer running. The timer status register indicates when the count is in progress (d0 = 1). This facilitates simple polling.

Here's the IOP16 code to blink an LED off and every second:

000    START    0x7800    IOW    #0x00    IO_00   WRITE TO LED    
001             0x2001    LRI    Reg0     0X01    TIME 1 SEC    
002             0x7006    IOW    Reg0     IO_06   STORE TO START TIMER    
003    WAITDUN  0x6104    IOR    Reg1     IO_04   READ TIMER    
004             0x8101    ARI    Reg1     0X01    CHECK BUSY    
005             0xDFFE    BNZ    WAITDUN                    
006             0x7900    IOW    #0x01    IO_00   WRITE TO LED    
007             0x2001    LRI    Reg0     0X01    TIME 1 SEC    
008             0x7006    IOW    Reg0     IO_06   STORE TO START TIMER    
009    WAITD2   0x6104    IOR    Reg1     IO_04   READ TIMER    
00a             0x8101    ARI    Reg1     0X01    CHECK BUSY    
00b             0xDFFE    BNZ    WAITD2                    
00c             0xE000    JMP    START